Phthalocyanines and naphthalocyanines are macrocylic compounds that have strong coloring power attributed to their alternating nitrogen and carbon atom central ring structures of porphyrin compounds (i.e., benzene-porphyrin and naphthalene-porphyrin compounds, respectively). As such, phthalocyanines and naphthalocyanines are useful in coloring agents with many applications in biology and chemistry as well as industry. The central nitrogen atoms of a pyrroline portion of the porphyrin compounds may be either complexed with a metal or are metal-free to provide further variations in color. For example, metal-free phthalocyanine has a blue-green color while copper-complexed phthalocyanine has a blue color (Pigment Blue 15). Other substitutions on the phthalocyanine and naphthalocyanine compounds invoke other colors as well. In general, these dyes exhibit absorption at wavelengths up to 1000 nm. Phthalocyanine and naphthalocyanine are chemically stable compounds that are normally not soluble in water or aqueous solutions. Water soluble groups can be added to increase the water solubility of the phthalocyanine and naphthalocyanine compounds. To solubilize either of their structures, one or both of highly ionic groups and soluble ethylene oxide groups can be attached to dissolve them in water. Unfortunately, commercial water soluble cyanine, phthalocyanine and naphthalocyanine compounds with near IR absorption have relatively poor stability in water or aqueous solution or do not have the appropriate absorption range. Any degradation in solution that changes their physical or chemical nature can destroy their conjugation, such that their characteristic absorption (color) may be lost.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.